header {
    display: block;
    margin: 0 auto;
    width: 500px;
    text-align: center;
}
header h1 {
    font-family: Arial;
    font-size: 60px;
    font-weight: bold;
}
header #newgamebutton {
    display: block;
    margin: 20px auto;
 
    width: 100px;
    padding: 10px 10px;
    background-color: #8f7a66;
 
    font-family: Arial;
    color: white;
 
    border-radius: 10px;
 
    text-decoration: none;
}
header #newgamebutton:hover {
    background-color: #9f8b77;
}
header p {
    font-family: Arial;
    font-size: 25px;
    margin: 20px auto;
}
#grid-container {
    width: 460px;
    height: 460px;
    padding: 20px;
 
    margin: 50px auto;
    background-color: #bbada0;
 
    border-radius: 10px;
    position: relative;
}
.grid-cell {
    width: 100px;
    height: 100px;
    border-radius: 6px;
    background-color: #ccc0b3;
 
    position: absolute;
}
.number-cell {
    border-radius: 6px;
 
    font-family: Arial;
    font-weight: bold;
    font-size: 60px;
    line-height: 100px;
    text-align: center;
 
    position: absolute;
}